1. Field of the Invention
The present invention relates to a semiconductor integrated circuit tester for testing a semiconductor integrated circuit (hereinafter, referred to as IC) including a memory or the like, and for determining whether the tested IC is a defective (failure) article or not, and more particularly, relates to a timing calibration apparatus and a timing calibration method in such an IC tester each being capable of conforming the timing at which a test pattern signal is applied to each of terminals of an IC under test and the timing at which a response signal outputted from each of terminals of the IC under test is fetched into or read in the IC tester, to a prescribed set value for each terminal.
2. Description of the Related Art
In an IC tester heretofore in use, there have been carried out a timing calibration for conforming the phase of a test pattern signal applied to each terminal (also called xe2x80x9cpinxe2x80x9d) of an IC under test (the timing at which the test pattern signal is applied to each terminal) with each other and a timing calibration for conforming the phase of a response signal when the response signal outputted from each terminal of the IC under test is fetched into or read in the IC tester (the timing at which the response signal is fetched into the IC tester) with each other.
As a calibration method of timing, there has been used a method in which a variable delay circuit previously inserted in the signal path or line for each terminal of the IC under test is adjusted in its delay time thereby to conform the delay time of each signal path with each other.
The following two methods are put to practical use as a method for measuring the delay time of a signal path or line, which will be explained.
(1) A method comprising the steps of: measuring a reflection time of a signal propagating through a signal path or line by utilization of a timing measuring function that the IC tester has; and measuring a propagation delay time of the signal path on the basis of the reflection time of the signal.
(2) A method comprising the steps of: bringing a probe into contact with each of terminals (pins) of an IC socket to which an IC under test is mounted when it is tested; supplying a calibration pulse having applied to each terminal of the IC socket to an oscilloscope through the probe; measuring the phase difference between the calibration pulse and a signal having the reference phase in the oscilloscope; and measuring a propagation delay time of the signal path through which the calibration pulse has propagated on the basis of the phase difference.
In case of using the measuring method (1) mentioned above, the reflected wave of the calibration pulse has an inferior quality in its waveform, and hence the accuracy of detecting the arrival of the reflection wave is deteriorated. Accordingly, there is a drawback that the calibration accuracy of timing is also lowered.
In the above-mentioned measuring method (2), since the phase difference between the signal to be measured and the reference signal is measured by the oscilloscope, the measuring accuracy is high. Accordingly, there is an advantage that the calibration of timing can be carried out with high accuracy. However, in case of using the above measuring method (2), the signal path that its timing calibration can be done by use of the measuring method (2) is limited to a signal path or line having a driver inserted therein which is capable of supplying a test pattern signal to an IC socket (hereinafter, referred to as driver included signal path), and a signal path or line through which a response signal outputted from an IC under test is propagated to a comparator (a signal path not including a driver) is excluded from a subject to be measured. Therefore, the signal path through which a response signal outputted from an IC under test is propagated (hereinafter, referred to as comparator included signal path) must be measured in its propagation delay time by using the above-mentioned measuring method (1) utilizing the reflected wave of the calibration pulse. As a result, in case of using the above measuring method (2), though the calibration accuracy of timing on the driver included signal path becomes high, the calibration accuracy of timing on the comparator included signal path remains inferior, and hence there is a drawback that the calibration accuracy of timing is deteriorated as a whole.
Moreover, in the above measuring method (2), an oscilloscope must be provided, which is entirely unnecessary in testing an IC. An oscilloscope is very expensive among others, which is constructed such that it has the accuracy and measurement band or range capable of measuring a signal from an IC tester, is of two input type and automatically measures the phase difference between two signals, and outputs data corresponding to the phase difference. Accordingly, a high expensive oscilloscope must be provided for only calibration of timing, which results in a drawback that an economic or financial defrayal is increased.
It is a first object of the present invention to provide a timing calibration apparatus and a timing calibration method in an IC tester each being capable of carrying out a calibration of timing on either a driver included signal path or a comparator included signal path with high accuracy by utilizing an optical pulse.
It is a second object of the present invention to provide a timing calibration apparatus and a timing calibration method in an IC tester each being capable of reducing the cost required to carry out a calibration of timing on any signal path.
In order to accomplish the aforesaid objects, there is provided, in a first aspect of the present invention, a timing calibration apparatus in an IC tester, the IC tester comprising: an IC socket on which an IC under test is to be mounted; signal paths including drivers respectively, each applying a calibration pulse to the IC socket; a probe to be sequentially contacted with terminals of the IC socket to take therein a calibration pulse applied to the IC socket; signal paths including comparating means respectively, each being connected with corresponding one of the terminals of the IC socket and being supplied through the IC socket with a calibration pulse having the reference phase generated from the probe; and timing calibration means for conforming a signal propagation time on each of the driver included signal paths to the reference value as well as conforming the applied timing of each of strobe pulses given to the comparating means to the predetermined reference phase of the calibration pulse, the timing calibration apparatus comprising: an optically driven type driver provided in the probe; and an optical drive signal supply means provided in the IC tester for supplying an optical drive signal to the optically driven type driver to generate the calibration pulse having the reference phase from the optically driven type driver.
In a second aspect of the present invention, there is provided a timing calibration apparatus in an IC tester, the IC tester comprising: an IC socket on which an IC under test is to be mounted; signal paths including drivers respectively, each applying a calibration pulse to the IC socket; a probe to be sequentially contacted with terminals of the IC socket. to take therein a calibration pulse applied to the IC socket; signal paths including comparating means respectively, each being connected with corresponding one of the terminals of the IC socket and being supplied through the IC socket with a calibration pulse having the reference phase generated from the probe; and timing calibration means for conforming a signal propagation time on each of the driver included signal paths to the reference value as well as conforming the applied timing of each of strobe pulses given to the comparating means to the predetermined reference phase of the calibration pulse, the timing calibration apparatus comprising: an optical modulator provided in the probe for modulating quantity of light in correspondence to the amplitude value of a calibration pulse taken in the probe from the IC socket; and a photoelectric converter provided in the IC tester for converting the quantity of light of the modulated optical signal transmitted from the optical modulator into an electric signal and supplying the electric signal to comparating means to which a strobe pulse is to be applied.
In a third aspect of the present invention, there is provided a timing calibration apparatus in an IC tester, the IC tester comprising: an IC socket on which an IC under test is to be mounted; signal paths including drivers respectively, each applying a calibration pulse to the IC socket; a probe to be sequentially contacted with terminals of the IC socket to take therein a calibration pulse applied to the IC socket; signal paths including comparating means respectively, each being connected with corresponding one of the terminals of the IC socket and being supplied through the IC socket with a calibration pulse having the reference phase generated from the probe; and timing calibration means for conforming a signal propagation time on each of the driver included signal paths to the reference value as well as conforming the applied timing of each of strobe pulses given to the comparating means to the predetermined reference phase of the calibration pulse, the timing calibration apparatus comprising: an optically driven type driver provided in the probe; an optical drive signal supply means provided in the IC tester for supplying an optical drive signal to the optically driven type driver to generate the calibration pulse having the reference phase from the optically driven type driver; an optical modulator provided in the probe for modulating quantity of light in correspondence to the amplitude value of a calibration pulse taken in the probe from the IC socket; and a photoelectric converter provided in the IC tester for converting the quantity of light of the modulated optical signal transmitted from the optical modulator into an electric signal and supplying the electric signal to comparating means to which a strobe pulse is to be applied.
In a preferred embodiment, the aforesaid optically driven type driver comprises: a plurality of photoconductive elements, each coming to electrically conductive state by applying light thereon; and a plurality of voltage supplies selected by the plurality of the photoconductive elements respectively, and for generating voltages corresponding to a logical signal.
The aforesaid optical modulator has such a structure that an electric field formed by the voltage of the calibration pulse is applied to either one of branched two optical waveguides, the direction of the electric field being orthogonal to the travelling direction of light, and the optical modulator is one of the type which modulates light by utilizing a delay of light caused by application of the electric field to light and varying the quantity of light of an interference light obtained by that the branched two lights have been unified.
An optical cable couples between the optically driven type driver and the optical drive signal supply means and between the optical modulator and the photoelectric converter.
In a fourth aspect of the present invention, there is provided a timing calibration method in an IC tester, the IC tester comprising: an IC socket on which an IC under test is to be mounted; signal paths including drivers respectively, each applying a calibration pulse to the IC socket; a probe to be sequentially contacted with terminals of the IC socket to take therein a calibration pulse applied to the IC socket; signal paths including comparating means respectively, each being connected with corresponding one of the terminals of the IC socket and being supplied through the IC socket with a calibration pulse having the reference phase generated from the probe; and timing calibration means for conforming a signal propagation time on each of the driver included signal paths to the reference value as well as conforming the applied timing of each of strobe pulses given to the comparating means to the predetermined reference phase of the calibration pulse, the timing calibration method comprising the steps of: converting, in the IC tester, an electric signal outputted from a waveform formatter into an optical signal; supplying the optical signal to a photoconductive element of an optically driven type driver provided in the probe; and generating the calibration pulse having the reference phase from the optically driven type driver.
In a fifth aspect of the present invention, there is provided a timing calibration method in an IC tester, the IC tester comprising: an IC socket on which an IC under test is to be mounted; signal paths including drivers respectively, each applying a calibration pulse to the IC socket; a probe to be sequentially contacted with terminals of the IC socket to take therein a calibration pulse applied to the IC socket; signal paths including comparating means respectively, each being connected with corresponding one of the terminals of the IC socket and being supplied through the IC socket with a calibration pulse having the reference phase generated from the probe; and timing calibration means for conforming a signal propagation time on each of the driver included signal paths to the reference value as well as conforming the applied timing of each of strobe pulses given to the comparating means to the predetermined reference phase of the calibration pulse, the timing calibration method comprising the steps of: modulating, in the probe, quantity of light of a propagating light in correspondence to the amplitude value of a calibration pulse taken in the probe from the IC socket; and converting the quantity of light of the modulated optical signal transmitted to the IC tester from the probe into an electric signal; and supplying the electric signal to comparating means and conforming the timing of the calibration pulse to the timing of a strobe pulse which is to be applied to the comparating means.
According to the present invention, since the IC tester and the test head to which the probe is attached are coupled with each other by an optical cable and a calibration pulse is converted into an optical signal which is received and transmitted between the IC tester and the test head or the probe, the optical signal is hardly deteriorated in its waveform, even if the optical cable is somewhat longer. Accordingly, the calibration of timing can be carried out with high accuracy.
Moreover, the timing of a calibration pulse taken in the probe and the timing of a calibration pulse supplied to the IC socket from the probe are measured by the timing measuring function that the IC tester is provided with. Accordingly, no high expensive instrument such as an oscilloscope is needed, and hence a cost required to carry out the calibration of timing can be reduced.
Furthermore, in accordance with the present invention, even in case of calibrating the applied timing of a strobe pulse which strobes a response signal inputted into comparating means of the IC tester, the applied timing of the strobe pulse is calibrated by generating a direct wave in the probe side. Therefore, the accuracy of the timing calibration can be improved.
In addition, in the probe provided on the test head side are housed only the optically driven type driver and the optical modulator, and no pyrogenic electric or electronic circuit elements or parts accompanied by heat are not used in the probe. Accordingly, a rise in temperature in the probe is very small, and temperature in the probe is stable. As a result, there occurs no problem that the propagation delay time of a signal varies due to a change of temperature. Thus, highly stable and reliable timing calibration apparatus and method can be provided.